Spinal manipulation (SM) is an effective treatment for low back pain, though the mechanisms by which it is effective remain elusive. It has been theorized that SM initiates a beneficial neurophysiological response by stimulating mechanically sensitive neurons in the facet joint capsule (FJC). The neurophysiological response during SM-like loads has been investigated in cat models, while the biomechanics of SM have been studied mostly in humans during in vivo or cadaveric studies. These data are not easily related because little is known about how the biomechanical response of the human lumbar spine during SM relates to that of the cat. The specific aim of the proposed study is to determine the mathematical relationship between the mechanical states of human and cat lumbar FJCs during SM. Cat cadaveric spines will be mechanically tested during simulated physiological motions and SM. A mathematical relationship will be established to relate cat lumbar FJC strain magnitudes to those obtained from prior studies in human cadaveric lumbar spines. Using this scaling relationship, the neurophysiological data obtained from cat models in future studies can be used to estimate how biomechanically similar motions would affect human FJC afferents.